Abstracts Category : Other

Improving high-frequency transit reliability : a casestudy of the MBTA Green Line through simulation and fieldexperiments of real-time control strategies; MBTA Green Line through simulation and fieldexperiments of real-time control strategies

by Joshua Javier Fabian

Service reliability is a major concern for publictransportation agencies. Transit services experience naturalvariability in scheduled service, due to factors such as trafficcongestion, irregular demand, multi-route and branching corridors,and operator behavior. This variability leads to irregularheadways, resulting in longer passenger waits and decreasedeffective capacity as gaps in service form. Real-time controlstrategies allow controllers to intervene at terminals and en routeto regulate headways and improve performance. This research teststhe effectiveness of holding control strategies on theMassachusetts Bay Transportation Authority (MBTA) Green Line inBoston, a complex, four-branch light rail line. A simulation modelis developed to estimate and compare the benefits of differentschedule-based and headway-based holding strategies. Dispatchingtrains at terminals to target headways is found to minimize waittime, and the addition of en route holding improves servicefurther, albeit slightly. The simulation results inform the designof a field experiment, in which headway-based dispatching isimplemented at a Green Line branch terminal. Terminal personnel areprovided with tablet computers showing departure times optimized byan even-headway policy. When optimized departure times are adheredto, peak-hour headway variability is reduced by 40%. The averagewait is shortened by 15% (30 seconds), and the 90th percentile waitis shortened by 21% (90 seconds). Compliance with the recommendeddeparture times in the experiment was hampered by various humanfactors and station features. During the experiment, only 49% oftrips left within 45 seconds of the departure times recommended bythe algorithm. These results show that adopting headway-baseddispatching at terminals promises significant benefits to serviceand passengers if operational changes are accompanied by improvedsupervision practices. This research fully supports the idea thattransit agencies, such as the MBTA, should allocate supervisoryresources for high-frequency services to prioritize terminalheadway control versus en route and schedule-basedstrategies.Advisors/Committee Members: John P. Attanucci, Frederick P. Salvucci, E. Snchez-Martnez (advisor).